Radio frequency amplifying circuit and power amplifying module

ABSTRACT

An radio frequency amplifying circuit includes an amplifying transistor configured to amplify a radio frequency signal input to a base of the amplifying transistor via a matching network to output the amplified radio frequency signal, a first bias transistor connected to the amplifying transistor based on a current-mirror connection to supply a bias to the amplifying transistor, and a second bias transistor connected to the base of the amplifying transistor based on an emitter-follower connection to supply a bias to the amplifying transistor.

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2013-057105, filed on Mar. 19, 2013, andJapanese patent application No. 2013-238245, filed on Nov. 18, 2013, thedisclosures of which are incorporated herein in its entirety byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radio frequency amplifying circuitand a power amplifying module including the radio frequency amplifyingcircuit.

2. Description of the Related Art

A mobile communication device such as a mobile phone uses a radiofrequency (RF) amplifying circuit to amplify power of a radio frequencysignal to be transmitted to a base station. Such an RF amplifyingcircuit includes an amplifying circuit that amplifies an RF signal and abias circuit that biases a transistor of the amplifying circuit. See,for example, Japanese Patent Publication 11-330866, hereinafter referredto as JP-A-11-330866.

FIG. 16 is a diagram showing a common configuration of an amplifyingcircuit and a bias circuit described in JP-A-11-330866 as a conventionaltechnique. An amplifying circuit 1601 amplifies an RF signal (RF_(IN))input to a base of the amplifying circuit 1601 and outputs the amplifiedRF signal (RF_(OUT)). A bias circuit 1602 biases a transistor 1603forming the amplifying circuit 1601 and has an emitter-followerconfiguration. In many cases, a battery voltage V_(BAT) is applied to acollector of a transistor 1604 forming the bias circuit 1602.

In such a configuration, when the transistors 1603 and 1604 are, forexample, heterojunction bipolar transistors (HBTs), a base-emittervoltage V_(BE) of each transistor is around 1.3 V. Thus, the batteryvoltage V_(BAT) needs to be about 2.8 V in order to drive the transistor1604. Thus, the minimum value of the battery voltage V_(BAT) isgenerally, for example, about 2.9 V.

In recent years, for mobile communication devices such as mobile phones,there has been a demand to reduce the minimum value of the batteryvoltage V_(BAT) down to, for example, about 2.5 V in order to increasecall time and communication time. However, in a configuration using thebias circuit 1602 of the emitter follower type as described above, thebattery voltage V_(BAT) needs to be about 2.8 V, precluding theabove-described demand from being met.

SUMMARY OF THE INVENTION

In view of such circumstances, preferred embodiments of the presentinvention provide a radio frequency amplifying circuit that is driven ata low voltage.

A preferred embodiment of the present invention provides a radiofrequency amplifying circuit including an amplifying transistorconfigured to amplify a radio frequency signal input to a base via amatching network to output the amplified radio frequency signal, a firstbias transistor connected to the amplifying transistor on the basis ofcurrent-mirror connection to supply a bias to the amplifying transistor,and a second bias transistor connected to the base of the amplifyingtransistor on the basis of emitter-follower connection to supply a biasto the amplifying transistor.

Preferred embodiments of the present invention enable the radiofrequency amplifying circuit to be driven at a low voltage for thereason described below.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an example of a configuration of atransmission unit including a power amplifying module according to apreferred embodiment of the present invention.

FIG. 2A is a diagram showing an example of a configuration of the poweramplifying module according to a preferred embodiment of the presentinvention.

FIG. 2B is a diagram showing another example of a configuration of thepower amplifying module according to a preferred embodiment of thepresent invention.

FIG. 2C is a diagram showing yet another example of a configuration ofthe power amplifying module according to a preferred embodiment of thepresent invention.

FIG. 3 is a diagram showing an example of a configuration of a controlvoltage generating circuit according to a preferred embodiment of thepresent invention.

FIG. 4A is a diagram showing an example of a configuration of an RFamplifying circuit according to a preferred embodiment of the presentinvention.

FIG. 4B is a diagram showing another example of a configuration of theRF amplifying circuit according to a preferred embodiment of the presentinvention.

FIG. 4C is a diagram showing yet another example of a configuration ofthe RF amplifying circuit according to a preferred embodiment of thepresent invention.

FIG. 5 is a diagram showing the principle of a bias supply.

FIG. 6 is a diagram showing a configuration of a switched capacitoraccording to a preferred embodiment of the present invention.

FIG. 7A is a diagram showing still another example of a configuration ofthe power amplifying module according to a preferred embodiment of thepresent invention.

FIG. 7B is a diagram showing further another example of a configurationof the power amplifying module according to a preferred embodiment ofthe present invention.

FIG. 7C is a diagram showing further another example of a configurationof the power amplifying module according to a preferred embodiment ofthe present invention.

FIG. 8 is a diagram showing another example of a configuration of thecontrol voltage generating circuit according to a preferred embodimentof the present invention.

FIG. 9A is a diagram showing still another example of a configuration ofthe RF amplifying circuit according to a preferred embodiment of thepresent invention.

FIG. 9B is a diagram showing further another example of a configurationof the RF amplifying circuit according to a preferred embodiment of thepresent invention.

FIG. 9C is a diagram showing further another example of a configurationof the RF amplifying circuit according to a preferred embodiment of thepresent invention.

FIG. 10 is a diagram showing an example of a relationship between acontrol voltage V_(CONT2) to and a gain property of the RF amplifyingcircuit shown in FIG. 4A.

FIG. 11 is a diagram showing an example of a relationship between acontrol voltage V_(CONT1) to and the gain property of the RF amplifyingcircuit shown in FIG. 9A.

FIG. 12 is a diagram showing an example of a change in gain propertyobserved when a control voltage V_(CONT2) is changed with the controlvoltage V_(CONT1) maintained at a predetermined level.

FIG. 13A is a diagram showing further another example of a configurationof the power amplifying module according to a preferred embodiment ofthe present invention.

FIG. 13B is a diagram showing further another example of a configurationof the power amplifying module according to a preferred embodiment ofthe present invention.

FIG. 13C is a diagram showing further another example of a configurationof the power amplifying module according to a preferred embodiment ofthe present invention.

FIG. 14A is a diagram showing further another example of a configurationof the power amplifying module according to a preferred embodiment ofthe present invention.

FIG. 14B is a diagram showing further another example of a configurationof the power amplifying module according to a preferred embodiment ofthe present invention.

FIG. 14C is a diagram showing further another example of a configurationof the power amplifying module according to a preferred embodiment ofthe present invention.

FIG. 15A is a diagram showing further another example of a configurationof the power amplifying module according to a preferred embodiment ofthe present invention.

FIG. 15B is a diagram showing further another example of a configurationof the power amplifying module according to a preferred embodiment ofthe present invention.

FIG. 15C is a diagram showing further another example of a configurationof the power amplifying module according to a preferred embodiment ofthe present invention.

FIG. 16 is a diagram showing a common configuration of an amplifyingcircuit and a bias circuit.

FIG. 17 is a diagram showing a variation of the RF amplifying circuitshown in FIG. 4A.

FIG. 18 is a diagram of simulation results indicating an example of arelationship between an amplified signal RF_(OUT) from and a gain of theconfiguration shown in FIG. 4A.

FIG. 19 is a diagram of simulation results indicating an example of arelationship between the amplified signal RF_(OUT) from and the gain ofthe configuration shown in FIG. 17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the drawings. FIG. 1 is a diagram showing an exampleof a configuration of a transmission unit including a power amplifyingmodule according to a preferred embodiment of the present invention. Atransmission unit 100 is preferably used in a mobile communicationdevice such as a mobile phone to transmit various signals for voice,data, and the like to a base station. The mobile communication devicealso includes a reception unit configured to receive signals from thebase station, which will not be described below.

As shown in FIG. 1, a transmission unit 100 includes a modulation unit101, a transmission power control unit 102, a power amplifying module103, a front end unit 104, and an antenna 105.

The modulation unit 101 modulates an input signal based on a modulationscheme such as High Speed Uplink Packet Access (HSUPA) or Long TermEvolution (LTE) to generate a radio frequency (RF) signal for wirelesstransmission. The RF signal is, for example, about several hundred MHzto several GHz in frequency.

The transmission power control unit 102 adjusts the power of the RFsignal based on a transmission power control signal to output theadjusted RF signal. The transmission power control signal is generated,for example, based on an adaptive power control (APC) signal transmittedby the base station. For example, the base station measures a signalfrom the mobile communication device to transmit the APC signal to themobile communication device as a command to adjust the transmissionpower of the mobile communication device to an appropriate level.

The power amplifying module 103 amplifies the power of the RF signal(RF_(IN)) output by the transmission power control unit 102 to a levelrequired for the power transmission to the base station, such that theamplified signal (RF_(OUT)) is output.

The front end unit 104 carries out, for example, filtering of theamplified signal and switching to and from a reception signal receivedfrom the base station. The amplified signal output by the front end unit104 is transmitted to the base station via the antenna 105.

FIG. 2A is a diagram showing an example of a configuration of the poweramplifying module 103. As shown in FIG. 2A, the power amplifying module103 includes a control voltage generating circuit 201, an RF amplifyingcircuit 202, and a matching network (MN) 203. Furthermore, the RFamplifying circuit 202 includes a bias circuit 211, an amplifyingcircuit 212, and a matching network 213.

In the configuration shown in FIG. 2A, the control voltage generatingcircuit 201 and the RF amplifying circuit 202 are preferably provided ondifferent substrates. For example, the control voltage generatingcircuit 201 preferably includes a MOS field-effect transistor (MOSFET).The RF amplifying circuit 202 can be configured using a bipolartransistor represented by a heterojunction bipolar transistor (HBT), forexample. When the HBT is used for the RF amplifying circuit 202, amaterial for a substrate providing the HBT may be, for example, SiGe,GaAs, InP, or GaN. Alternatively, the control voltage generating circuit201 and the RF amplifying circuit 202 may be provided on the samesubstrate.

The control voltage generating circuit 201 generates, from the batteryvoltage V_(BAT), a control voltage V_(CONT) supplied to the bias circuit211.

The bias circuit 211 uses the control voltage V_(CONT) supplied by thecontrol voltage generating circuit 201 to bias a transistor of theamplifying circuit 212.

The amplifying circuit 212 amplifies the input RF signal (RF_(IN)) tooutput the amplified RF signal RF_(OUT). Each of the matching networks213 and 203, provided before and after the amplifying circuit 212,respectively, is adapted to match an input impedance with an outputimpedance. Each of the matching networks 213 and 203 preferablyincludes, for example, a capacitor or an inductor.

A power supply voltage supplied to the RF amplifying circuit 202 may bethe battery voltage V_(BAT) as shown in FIG. 2A. Furthermore, the powersupply voltage supplied to the RF amplifying circuit 202 may be, forexample, a voltage V_(CC) of a predetermined level generated from thebattery voltage V_(BAT) via a DCDC converter, as shown in FIG. 2B.Moreover, as shown in FIG. 2C, the battery voltage V_(BAT) may be apower supply voltage supplied to the bias circuit 211 and the voltageV_(CC) may be a power supply voltage supplied to the amplifying circuit212.

An example of a configuration of the control voltage generating circuit201 and the RF amplifying circuit 202, which provide the poweramplifying module 103, will be described.

FIG. 3 is a diagram showing an example of a configuration of the controlvoltage generating circuit 201. As shown in FIG. 3, the control voltagegenerating circuit 201 can be configured using a band gap circuit 301,an operational amplifier 302, and resistors 303 and 304.

The band gap circuit 301 generates, from the power supply voltage (inFIG. 3, the battery voltage V_(BAT)), a band gap reference voltageV_(BG) that is independent of a variation in temperature or power supplyvoltage. A reference voltage V_(BG) output by the band gap circuit is,for example, about 1.2 V.

The operational amplifier 302 and the resistors 303 and 304 provide anon-inverting amplifying circuit and amplify the reference voltageV_(BG) using a gain that is dependent on the resistance value of theresistors 303 and 304 to generate a control voltage V_(CONT) The controlvoltage V_(CONT) may be, for example, about 2.35 V. A transistorproviding the operational amplifier 302 may be, for example, a MOSFET.Alternatively, the transistor providing the operational amplifier 302may be a bipolar transistor.

Furthermore, the control voltage generating circuit 201 may beconfigured to be able to adjust the control voltage V_(CONT) in order toregulate the gain of the amplifying circuit 212. For example, thecontrol voltage generating circuit 201 can adjust the control voltageV_(CONT) by changing the resistance value of the resistor 303 or theresistor 304 depending on an externally input control signal.

FIG. 4A is a diagram showing an example of a configuration of the RFamplifying circuit 202 shown in FIG. 2A. Furthermore, FIG. 4B and FIG.4C are diagrams showing examples of configurations of the RF amplifyingcircuit 202 shown in FIG. 2B and FIG. 2C. The configurations of the RFamplifying circuit 202 in FIG. 4A to FIG. 4C are equivalent except thatdifferent types of power supply voltages are supplied to the respectiveconfigurations. Thus, an example of a configuration of the RF amplifyingcircuit 202 will be described with reference to FIG. 4A. As describedabove, the RF amplifying circuit 202 includes the bias circuit 211, theamplifying circuit 212, and the matching network (capacitor) 213.

The bias circuit 211 can be configured to include transistors 401 to 403and resistors 404 to 409. The transistors 401 to 403 are, for example,bipolar transistors such as HBTs. Such a configuration allows the biascircuit 211 to supply a bias to the amplifying circuit 212. The biascircuit 211 will be described below in detail.

The amplifying circuit 212 can be configured to include a transistor 411(amplifying transistor) and an inductor 412. The transistor 411 is, forexample, a bipolar transistor such as an HBT.

As shown in FIG. 4A, an RF signal (RF_(IN)) is input to a base of thetransistor 411 via the matching network (capacitor) 213. A bias outputof the bias circuit 211 is connected to the base of the transistor 411.Furthermore, the battery voltage V_(BAT) is applied to one end of theinductor 412, and the other end of the inductor 412 is connected to acollector of the transistor 411. The amplified signal RF_(OUT) is outputfrom the collector of the transistor 411 via the matching network 203.

The bias circuit 211 will be described in detail. As shown in FIG. 4A,the transistor 401 (bias transistor) is diode-connected, and a base ofthe transistor 401 is connected to the base of the transistor 411 viathe resistor 405. Furthermore, the control voltage V_(CONT) is appliedto a collector of the transistor 401 via the resistor 404. That is, thetransistor 401 is connected to the transistor 411 on the basis ofcurrent-mirror connection. In other words, the transistors 401 and 411provide a current mirror circuit. Consequently, a current flowingthrough the transistor 401 allows a current dependent on the size ratioof the transistors 401 and 411 to flow through the transistor 411.

As described above, the transistor 401 is configured to supply a bias tothe transistor 411 connected to the transistor 401 on the basis of acurrent-mirror connection. In this case, the transistor 401 is groundedat an emitter thereof. Thus, even when the control voltage V_(CONT) isequal to about a base-emitter voltage V_(BE) of the transistor 401, acurrent is passed through the transistor 401.

However, the current flowing through the transistor 411 needs to beincreased consistently with the signal level of the RF signal (RF_(IN)).However, it may be impossible that a large current is provided only by abias from the current mirror circuit. Thus, for a bias supply in a casewhere the signal level of the RF signal (RF_(IN)) is higher than apredetermined level, the transistor 402 is provided which is connectedto the transistor 411 on the basis of the emitter-follower connection.

As shown in FIG. 4A, the control voltage V_(CONT) is applied to a baseof the transistor 402 (bias transistor) via the resistor 406.Furthermore, the battery voltage V_(BAT) is applied to a collector ofthe transistor 402. An emitter of the transistor 402 is connected to thebase of the transistor 411 via the resistor 407. When the base-emittervoltage V_(BE) of each of the transistors 411 and 402 is assumed to beabout 1.3 V, a voltage V_(BIAS) applied to the base of the transistor402 needs to be higher than about 2.7 V in order to constantly drive thetransistor 402, for example. Thus, if the control voltage V_(CONT) is,for example, 2.35 V, the transistor 402 cannot constantly be driven.

As described above, the bias circuit 211 fails to constantly drive thetransistor 402. However, in a region in which the RF signal (RF_(IN)) isat a high signal level, the transistor 402 is driven to supply a bias tothe transistor 411. The principle by which the transistor 402 supplies abias will be described below.

FIG. 5 is a diagram illustrating the principle by which the transistor402 supplies a bias to the transistor 411. As shown in FIG. 5, thevoltage V_(BIAS) is applied to the base of the transistor 402. If thecontrol voltage V_(CONT) supplied by the control voltage generatingcircuit is, for example, about 2.35 V, the voltage V_(BIAS) is equal toor lower than about 2.35 V. Thus, with the base-emitter voltage V_(BE)of each of the transistor 402 and the transistor 411 taken into account,the transistor 402 cannot constantly be kept on.

As shown in FIG. 5, the RF signal (RF_(IN)) is input to the base of thetransistor 411 via the capacitor 213. Thus, in a region where the RFsignal (RF_(IN)) is negative, the difference in potential between thebase and emitter of the transistor 402 is significant. In a region wherethe signal level of the RF signal (RF_(IN)) is higher than thepredetermined level, the potential difference is more significant thanthe base-emitter voltage V_(BE) of the transistor 402, which is thusturned on. On the other hand, the transistor 411 is turned off in theregion where the RF signal (RF_(IN)) is negative.

Furthermore, in a region where the RF signal (RF_(IN)) is positive, thedifference in potential between the base and emitter of the transistor402 decreases, thus turning the transistor 402 off. On the other hand,the transistor 411 is turned on in a region where the RF signal(RF_(IN)) is positive.

The capacitor 213 is connected to the base of the transistor 411, andthus, in the region where the signal level of the RF signal (RF_(IN)) ishigher than the predetermined level, the transistors 402 and 411 and thecapacitor 213 can be considered to be equivalent to a switched capacitorin terms of a DC, as shown in FIG. 6.

When the frequency of the RF signal (RF_(IN)) is denoted by f_(RE) andthe capacitance of the capacitor 213 is denoted by C_(IN), theresistance value of the switched capacitor shown in FIG. 6 is denoted by1/(f_(RE)·C_(IN)). Thus, a DC bias currentI_(BIAS)=V_(BIAS)·f_(RF)·C_(IN) is supplied to the base of thetransistor 411. Thus, in the region where the signal level of the RFsignal (RF_(IN)) is higher than the predetermined level, the transistor411 is supplied not only with a bias from the transistor 401 connectedto the transistor 411 on the basis of the current-mirror connection butalso with a bias from the transistor 402 connected to the transistor 411on the basis of the emitter-follower connection. Such a configurationenables the transistor 411 to be supplied with a bias even when thecontrol voltage V_(CONT) is, for example, about 2.35 V. That is, the RFamplifying circuit 202 is configured to be driven at a low voltage.

With reference back to FIG. 4A, a voltage adjusting circuit 420including the transistor 403 and the resistors 408 and 409 will bedescribed. The transistor 403 is connected to the base of the transistor402 at a collector of the transistor 403 and grounded at an emitter ofthe transistor 403. The resistor 408 is connected between the base andcollector of the transistor 403. The resistor 409 is connected betweenthe base and emitter of the transistor 403. When the base-emittervoltage of the transistor 403 is denoted by V_(BE) and the resistancevalues of the resistors 408 and 409 are denoted by R₁ and R₂, thevoltage of the collector of the transistor 403, that is, the voltageV_(BIAS) applied to the base of the transistor 402, is equal to V_(BE)(1+(R₁/R₂)). Thus, the voltage V_(BIAS) applied to the base of thetransistor 402 can be set to a predetermined level that is dependent onthe resistance values of the resistors 408 and 409. Furthermore, inconnection with the base-emitter voltage V_(BE), the transistor 403 hasa temperature property equivalent to the temperature property of thetransistor 402. Consequently, the voltage V_(BIAS) can be adjustedaccording to the temperature property of the transistor 402.Additionally, a possible variation in diode potential caused by aprocess is compensated for. This allows the bias supplied to thetransistor 411 by the transistor 402 to be restrained from being changedby temperature, improving the linearity of the RF amplifying circuit202.

FIG. 7A to FIG. 7C are diagrams showing other examples of configurationsof the power amplifying module 103. The configurations of the poweramplifying module 103 in FIG. 7A to FIG. 7C are equivalent except thatdifferent types of power supply voltages are supplied to an RFamplifying circuit 702. With reference to FIG. 7A, an example of aconfiguration of the power amplifying module 103 will be described.Components of the power amplifying module in FIG. 7A which areequivalent to corresponding components shown in FIG. 2A are denoted bythe same reference numerals and will not be described below. As shown inFIG. 7A, a power amplifying module 103A includes a control voltagegenerating circuit 701 and RF amplifying circuit 702 instead of thecontrol voltage generating circuit 201 and RF amplifying circuit 202shown in FIG. 2A. The control voltage generating circuit 701 generatesand supplies two control voltages V_(CONT1) and V_(CONT2) to a biascircuit 711. The bias circuit 711 biases the transistor providing theamplifying circuit 212 based on the control voltages V_(CONT1) andV_(CONT2).

FIG. 8 is a diagram showing an example of a configuration of the controlvoltage generating circuit 701. As shown in FIG. 8, the control voltagegenerating circuit 701 includes a band gap circuit 301, operationalamplifiers 801 and 802, and resistors 803 to 806. The band gap circuit301 is equivalent to the band gap circuit 301 shown in FIG. 3.

In the configuration shown in FIG. 8, the operational amplifier 801 andthe resistors 803 and 804 provide a voltage generating circuit thatgenerates a control voltage V_(CONT1). Furthermore, the operationalamplifier 802 and the resistors 805 and 806 provide a voltage generatingcircuit that generates a control voltage V_(CONT2). An operation ofgenerating the control voltages V_(CONT1) and V_(CONT2) is equivalent tothe corresponding operation in the control voltage generating circuit201 shown in FIG. 3 and will thus not be described below.

FIG. 9A is a diagram showing an example of a configuration of the RFamplifying circuit 702 shown in FIG. 7A. Furthermore, FIG. 9B and FIG.9C show examples of configurations of the RF amplifying circuit 702shown in FIG. 7B and FIG. 7C, respectively. The configurations of the RFamplifying circuit 702 in FIG. 9A to FIG. 9C are equivalent except thatdifferent power supply voltages are supplied to the respectiveconfigurations. Thus, an example of a configuration of the RF amplifyingcircuit 702 will be described with reference to FIG. 9A. Components ofthe RF amplifying circuit in FIG. 9A which are equivalent tocorresponding components shown in FIG. 4A are denoted by the samereference numerals and will not be described below. As shown in FIG. 9A,the RF amplifying circuit 702 includes the bias circuit 711 instead ofthe bias circuit 211 in FIG. 4A.

An internal configuration of the bias circuit 711 is equivalent to theinternal configuration of the bias circuit 211 shown in FIG. 4A exceptthat different control voltages are externally supplied to the biascircuits 711 and 211, respectively. Specifically, in the bias circuit711, the control voltage V_(CONT1) is applied to the collector side ofthe transistor 401, and the control voltage V_(CONT2) is applied to thebase side of the transistor 402. Thus, in the bias circuit 711, a biasfrom the transistor 401 and a bias from the transistor 402 arecontrolled by the different control voltages. When the two controlvoltages V_(CONT1) and V_(CONT2) are thus used to control the biases,the linearity of the RF amplifying circuit 702 is significantlyimproved. This will be described below.

In the RF amplifying circuit, the control voltages may be changed inorder to adjust the gain of the RF amplifying circuit. FIG. 10 is adiagram showing a relationship between the control voltage V_(CONT) toand a gain property of the RF amplifying circuit 202 shown in FIG. 4A.As shown in FIG. 10, in the RF amplifying circuit 202, a reduction incontrol voltage V_(CONT) may degrade the linearity. This is because theRF amplifying circuit 202 uses the single control voltage V_(CONT) tocontrol the bias from the transistor 401 and the bias from thetransistor 402. When a base-collector potential of the transistor 401 isreduced in order to lower the gain, the base potential of the transistor402 simultaneously decreases. In this case, the transistor 402 fails tostart operating unless a larger RF signal is input to the RF amplifyingcircuit. If only the transistor 401 provides a bias, a current flowingthrough the transistor 411 is limited even with an increase in RF inputpower, thus reducing the gain of the amplifier. When the transistor 402fails to start operating before the gain decreases, the linearitydecreases as shown in FIG. 10.

In order to demonstrate this phenomenon, a relationship between thecontrol voltage V_(CONT1) to and the gain property of the RF amplifyingcircuit 702 was experimentally checked which relationship was observedwhen the bias circuit 711 shown in FIG. 9A was adopted. In theexperiments, the control voltage V_(CONT2) was maintained at apredetermined level (for example, about 2.35 V) regardless of thecontrol voltage V_(CONT1). FIG. 11 is a diagram showing the results ofthe experiments. As shown in FIG. 11, when the control voltage V_(CONT1)was reduced with the control voltage V_(CONT2) maintained at thepredetermined level, the linearity was successfully improved compared tothe linearity in the case shown in FIG. 10.

Furthermore, FIG. 12 is a diagram showing an example of a change in gainproperty observed when the control voltage V_(CONT2) is changed, withthe control voltage V_(CONT1) maintained at a predetermined level (forexample, about 2.35 V) in the RF amplifying circuit 702. FIG. 12 showsthat the linearity is degraded by reducing the control voltage V_(CONT2)from, for example, about 2.35 V. This result also indicates thatmaintaining the control voltage V_(CONT2) at the predetermined level(for example, about 2.35 V) is effective for improving the linearity ofthe RF amplifying circuit 702.

In the RF amplifying circuit 702, the voltage V_(BIAS) applied to thebase of the transistor 402 is determined by the transistor 403 and theresistors 408 and 409. Specifically, when the base-emitter voltage ofthe transistor 403 is denoted by V_(BE) and the resistance values of theresistors 408 and 409 are denoted by R₁ and R₂, respectively, thevoltage V_(BIAS) applied to the base of the transistor 402 is equal toV_(BE) (1+(R₁/R₂)). Thus, when, for example, V_(BE) is about 1.3 V,V_(BIAS) can be set to about 2.35 V by setting the control voltageV_(CONT2) equal to or higher than about 2.35 V and setting R₁ and R₂ toabout 8 kΩ and about 10 kΩ, respectively.

FIG. 13A to FIG. 13C are diagrams showing other examples ofconfigurations of the power amplifying module 103. The configurations ofthe power amplifying module 103 in FIG. 13A to FIG. 13C are equivalentexcept that different types of power supply voltages are supplied to therespective configurations. Thus, an example of a configuration of thepower amplifying module 103 will be described with reference to FIG.13A. Components of the power amplifying module in FIG. 13A which areequivalent to corresponding components shown in FIG. 2A are denoted bythe same reference numerals and will not be described below. As shown inFIG. 13A, a power amplifying module 103B includes the RF amplifyingcircuit 1301 instead of the RF amplifying circuit 202 in FIG. 2A.

The RF amplifying circuit 1301 includes two amplifying circuits 1311 and1312. Each of the amplifying circuits 1311 and 1312 is configuredequivalently to the amplifying circuit 212 shown in FIG. 4A.Furthermore, the RF amplifying circuit 1301 includes bias circuits 1313and 1314 for the amplifying circuits 1311 and 1312, respectively. Eachof the bias circuits 1313 and 1314 is configured equivalently to thebias circuit 211 shown in FIG. 4A. The bias circuits 1313 and 1314 aresupplied with the control voltage V_(CONT). Additionally, the RFamplifying circuit 1301 includes matching networks 1315 and 1316configured to match an input impedance with an output impedance.

As shown in FIG. 13A, the provision of the two amplifying circuitsenables an increase in the gain of the RF amplifying circuit. Even sucha configuration allows the bias circuits 1313 and 1314 to operate at allow voltage of, for example, about 2.35 V similarly to the bias circuit211 shown in FIG. 4A. That is, the RF amplifying circuit 1301 isconfigured to be driven at a low voltage.

FIG. 14A to FIG. 14C are diagrams showing other examples ofconfigurations of the power amplifying module 103. The configurations ofthe power amplifying module 103 in FIG. 14A to FIG. 14C are equivalentexcept that different types of power supply voltages are supplied to anRF amplifying circuit 1401. Thus, an example of a configuration of thepower amplifying module 103 will be described with reference to FIG.14A. Components of the power amplifying module in FIG. 14A which areequivalent to corresponding components shown in FIG. 13A are denoted bythe same reference numerals and will not be described below. As shown inFIG. 14A, a power amplifying module 103C includes the control voltagegenerating circuit 701 and the RF amplifying circuit 1401 instead of thecontrol voltage generating circuit 201 and RF amplifying circuit 1301shown in FIG. 13A. The control voltage generating circuit 701 isconfigured equivalently to the control voltage generating circuit 701shown in FIG. 8. The RF amplifying circuit 1401 is configuredequivalently to the RF amplifying circuit 1301 shown in FIG. 13A exceptthat the RF amplifying circuit 1401 has input terminals for the controlvoltages V_(CONT1) and V_(CONT2). In such a configuration, the biascircuits 1313 and 1314 are supplied with the different control voltagesV_(CONT1) and V_(CONT2) respectively. This enables bias control in theRF amplifying circuit 1401 to be precisely performed.

FIG. 15A to FIG. 15C are diagrams showing other examples ofconfigurations of the power amplifying module 103. The configurations ofthe power amplifying module 103 in FIG. 15A to FIG. 15C are equivalentexcept that different types of power supply voltages are supplied to anRF amplifying circuit 1501. Thus, an example of a configuration of thepower amplifying module 103 will be described with reference to FIG.15A. Components of the power amplifying module in FIG. 15A which areequivalent to corresponding components shown in FIG. 14A are denoted bythe same reference numerals and will not be described below. As shown inFIG. 15A, a power amplifying module 103D includes the RF amplifyingcircuit 1501 instead of the RF amplifying circuit 1401 shown in FIG.14A.

The RF amplifying circuit 1501 includes bias circuits 1511 and 1512instead of the bias circuits 1313 and 1314 in the RF amplifying circuit1401 shown in FIG. 14A. Each of the bias circuits 1511 and 1512 isconfigured equivalently to the bias circuit 711 shown in FIG. 9A. Thebias circuits 1511 and 1512 are supplied with the control voltagesV_(CONT1) and V_(CONT2). Even when two amplifying circuits are providedas described above, effects similar to the effects of the circuitconfiguration shown in FIG. 9A by preparing two control voltagessupplied to each of the two bias circuits. The power amplifying modulemay be configured such that the control voltages V_(CONT1) and V_(CONT2)supplied to the bias circuit 1511 are controlled separately from thecontrol voltages V_(CONT1) and V_(CONT2) supplied to the bias circuit1512.

FIG. 17 is a diagram showing a variation of the RF amplifying circuit202 shown in FIG. 4A. Components of this circuit in FIG. 17, which areequivalent to corresponding components shown in FIG. 4A, are denoted bythe same reference numerals as those in FIG. 4A and explanation thereofis omitted below. As shown in FIG. 17, the RF amplifying circuit 202includes a capacitor 1700 in addition to the components shown in FIG. 4.The capacitor 1700 is connected to the base of the transistor 401 at oneend of the capacitor 1700 and grounded at the other end of the capacitor1700. Providing the capacitor 1700 in this manner allows the linearityof the RF amplifying circuit 202 to be improved. This will be describedbelow.

FIG. 18 is a diagram of simulation results showing an example of arelation between the amplified signal RF_(OUT) from and the gain of theconfiguration shown in FIG. 4A (the configuration without the capacitor1700). As shown in FIG. 18, the gain slightly decreases in a regionwhere the amplified signal RF_(OUT) is at a medium signal level (in FIG.18, nearly 20 dBm).

As described above, in the RF amplifying circuit 202 shown in FIG. 4A, abias is supplied by the transistor 401 connected to the transistor 411on the basis of a current-mirror connection in a region where the RFsignal (RF_(IN)) is at a low signal level (that is, the region where theamplified signal (RF_(OUT)) is at a low signal level). Furthermore, in aregion where the RF signal (RF_(IN)) is at a high signal level (that is,the region where the amplified signal (RF_(OUT)) is at a high signallevel), in addition to the bias based on the current mirror, a bias issupplied by the transistor 402 connected to the transistor 411 on thebasis of an emitter-follower connection. The decrease in gain shown inFIG. 18 is expected to be due to a temporary insufficiency of bias, forexample, at a timing when the supply of the bias based on the emitterfollower is started.

FIG. 19 is a diagram of simulation results showing an example of arelationship between the amplified signal RF_(OUT) from and the gain ofthe configuration shown in FIG. 17 (the configuration with the capacitor1700). In the RF amplifying circuit 202 shown in FIG. 17, charge isaccumulated in the capacitor 1700 while the bias based on the currentmirror is being supplied. The charge accumulated in the capacitor 1700is supplied to the base of the transistor 411 to compensate for theinsufficiency of bias. Thus, as shown in FIG. 19, the decrease in gainobserved in FIG. 18 is reversed, allowing the linearity of the RFamplifying circuit 202 to be improved.

In the described configuration, the capacitor 1700 is added to the RFamplifying circuit 202 shown in FIG. 4A. Similarly, when the capacitor1700 is added to the RF amplifying circuit 202 shown in FIG. 4B and FIG.4C, the linearity is improved. This also applies to the RF amplifyingcircuit 202 with a multistage configuration.

Various preferred embodiments of the present invention have beendescribed. Even when the control voltage V_(CONT) is a low voltage ofabout 2.35 V, various preferred embodiments of the present inventionwork as follows. In a region where the RF signal (RF_(IN)) is at a lowlevel, a bias is supplied by the bias transistor connected to theamplifying transistor on the basis of a current-mirror connection. In aregion where the RF signal (RF_(IN)) is at a high level, a bias issupplied by the bias transistor connected to the amplifying transistoron the basis of an emitter-follower connection. That is, the RFamplifying circuit is configured to be driven at a low voltage.

Various preferred embodiments of the present invention also individuallycontrol the control voltage supplied to the bias transistor connected tothe amplifying transistor on the basis of the current-mirror connectionand the control voltage supplied to the bias transistor connected to theamplifying transistor in an emitter follower transistor. Thus, the gainof the RF amplifying circuit is adjustable simply by changing only thecontrol voltage supplied to the bias transistor connected to theamplifying transistor on the basis of the current-mirror connectionwhile the control voltage supplied to the bias transistor connected tothe amplifying transistor in an emitter follower transistor ismaintained at a predetermined level. When the control voltage suppliedto the bias transistor connected to the amplifying transistor in anemitter follower transistor is thus maintained at the predeterminedlevel, the linearity of the RF amplifying circuit is significantlyimproved.

The same control voltage may be supplied both to the bias transistorconnected to the amplifying transistor on the basis of thecurrent-mirror connection and to the bias transistor connected to theamplifying transistor on the basis of the emitter-follower connection.This allows a single terminal to be used to supply the control voltage,enabling a reduction in chip size.

Furthermore, various present preferred embodiments of the presentinvention allow the control voltage supplied to the bias transistorconnected to the amplifying transistor on the basis of theemitter-follower connection to be adjusted according to the temperatureproperty of the bias transistor. This enables the bias supplied to theamplifying transistor by the bias transistor to be prevented fromvarying depending on temperature, allowing the linearity of the RFamplifying circuit to be improved.

Additionally, various preferred embodiments of the present inventionachieve the above-described effects and advantages even when twoamplifying circuits are provided. This also applies to provision ofthree or more amplifying circuits.

In addition, various preferred embodiments of the present inventionprovide a capacitor connected at one end thereof to the bias transistorconnected to the amplifying transistor on the basis of a current-mirrorconnection and grounded at the other end thereof. This enables apossible insufficiency of bias to be compensated for, allowing thelinearity of the RF amplifying circuit to be improved.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A radio frequency amplifying circuit comprising:an amplifying transistor configured to amplify a radio frequency signalinput to a base of the amplifying transistor via a matching network tooutput an amplified radio frequency signal; a first bias transistorconnected to the amplifying transistor based on a current-mirrorconnection to supply a bias to the amplifying transistor; and a secondbias transistor connected to the base of the amplifying transistor basedon an emitter-follower connection to supply a bias to the amplifyingtransistor.
 2. The radio frequency amplifying circuit according to claim1, wherein an input terminal for a first control voltage applied to acollector side of the first bias transistor and an input terminal for asecond control voltage applied to a base side of the second biastransistor are independent and separate from each other.
 3. The radiofrequency amplifying circuit according to claim 1, wherein an inputterminal for a first control voltage applied to a collector side of thefirst bias transistor and an input terminal for a second control voltageapplied to a base side of the second bias transistor are defined by acommon terminal.
 4. The radio frequency amplifying circuit according toclaim 1, further comprising a voltage adjusting circuit configured toadjust the voltage applied to the base of the second bias transistoraccording to a temperature property of the second bias transistor. 5.The radio frequency amplifying circuit according to claim 4, wherein thevoltage adjusting circuit includes a voltage adjusting transistor havinga temperature property of a base-emitter voltage that is equivalent to atemperature property of a base-emitter voltage of the second biastransistor, and is configured to supply a voltage in accordance with thebase-emitter voltage of the voltage adjusting transistor to the base ofthe second bias transistor.
 6. The radio frequency amplifying circuitaccording to claim 1, further comprising a capacitor connected to a baseof the first bias transistor at one end of the capacitor and grounded atanother end of the capacitor.
 7. The radio frequency amplifying circuitaccording to claim 1, further comprising: a second amplifying transistorconfigured to amplify a radio frequency signal input, by the amplifyingtransistor, to a base of the second amplifying transistor via a matchingnetwork; a third bias transistor connected to the second amplifyingtransistor based on a current-mirror connection to supply a bias to thesecond amplifying transistor; and a fourth bias transistor connected toa base of the second amplifying transistor based on an emitter-followerconnection to supply a bias to the second amplifying transistor.
 8. Theradio frequency amplifying circuit according to claim 7, wherein aninput terminal for a first control voltage applied to collector sides ofthe first and third bias transistors and an input terminal for a secondcontrol voltage applied to base sides of the second and fourth biastransistors are independent and separate from each other.
 9. The radiofrequency amplifying circuit according to claim 7, wherein an inputterminal for a first control voltage applied to collector sides of thefirst and third bias transistors and an input terminal for a secondcontrol voltage applied to base sides of the second and fourth biastransistors are defined by a common terminal.
 10. The radio frequencyamplifying circuit according to claim 7, further comprising a voltageadjusting circuit configured to adjust the voltage applied to the basesof the second and fourth bias transistors according to temperatureproperties of the transistors.
 11. The radio frequency amplifyingcircuit according to claim 7, further comprising: a first capacitorconnected to a base of the first bias transistor at one end of the firstcapacitor and grounded at another end of the first capacitor; and asecond capacitor connected to a base of the third bias transistor at oneend of the second capacitor and grounded at another end of the secondcapacitor.
 12. The radio frequency amplifying circuit according to claim1, wherein at least one of the amplifying transistor, the first biastransistor, and the second bias transistor is a heterojunction bipolartransistor.
 13. A power amplifying module comprising: the radiofrequency amplifying circuit according to claim 1; and a control voltagegenerating circuit configured to generate a control voltage supplied tothe radio frequency amplifying circuit.
 14. The radio frequencyamplifying circuit according to claim 2, further comprising a voltageadjusting circuit configured to adjust the voltage applied to the baseof the second bias transistor according to a temperature property of thesecond bias transistor.
 15. The radio frequency amplifying circuitaccording to claim 3, further comprising a voltage adjusting circuitconfigured to adjust the voltage applied to the base of the second biastransistor according to a temperature property of the second biastransistor.
 16. The radio frequency amplifying circuit according toclaim 14, wherein the voltage adjusting circuit includes a voltageadjusting transistor having a temperature property of a base-emittervoltage that is equivalent to a temperature property of a base-emittervoltage of the second bias transistor, and is configured to supply avoltage in accordance with the base-emitter voltage of the voltageadjusting transistor to the base of the second bias transistor.
 17. Theradio frequency amplifying circuit according to claim 15, wherein thevoltage adjusting circuit includes a voltage adjusting transistor havinga temperature property of a base-emitter voltage that is equivalent to atemperature property of a base-emitter voltage of the second biastransistor, and is configured to supply a voltage in accordance with thebase-emitter voltage of the voltage adjusting transistor to the base ofthe second bias transistor.
 18. The radio frequency amplifying circuitaccording to claim 2, further comprising a capacitor connected to a baseof the first bias transistor at one end of the capacitor and grounded atanother end of the capacitor.
 19. The radio frequency amplifying circuitaccording to claim 3, further comprising a capacitor connected to a baseof the first bias transistor at one end of the capacitor and grounded atanother end of the capacitor.
 20. The radio frequency amplifying circuitaccording to claim 4, further comprising a capacitor connected to a baseof the first bias transistor at one end of the capacitor and grounded atanother end of the capacitor.